You should support Mac Game development, even if the port is bad or 80% of the quality of the PC version. I have over 90 Mac Games on Steam alone, with Origin and Mac Game Store adding another 10 titles or so.
Buy it, install it and play it. Why? because if you install it, the mac game developer will get part of their share of income from the sale price. I believe I read it here somewhere (feral interactive dev - i think it was eddie?) that if you don't install a game within a week that it was purchased under "Steamplay" the mac devs don't get their share of the money, and your purchase is accounted to "PC" bought game - not Mac. If you want more mac supported games, your going to need to show that purchases are being made to be played on a Mac.
Why is this important?
Because not too long ago, Mac Game Development was too far and few between, ports were even rarer. We had no Steam, everything was mostly shareware and you had Id, EPIC and Blizzard as the major Mac game developers. It was a sad time, so support your Mac game developers, otherwise we'll just be neglected again.
FYI - I have a nMacPro - D700, 32GB RAM - I have Bootcamp and can CrossFireX games in Windows which makes the games even better, but I still install the game on the Mac first, play it then install on windows to see the difference.
Most recent game purchase was ARK - Survival Evolved, sure its unplayable at high details on OS X, but I bought it to support mac game developers and play in Window-ed mode (its faster than full screen), 1280x720 and mid settings on OS X, lol. - it works.